1. Field of the Invention
The present invention relates to a silicon focus ring for a plasma etching, for example, used for a dry etching apparatus used in a fabrication process of a semiconductor device.
2. Description of the Related Art
For example, in fabrication of such as a semiconductor device, apparatuses utilizing plasma are mostly used when a silicon wafer is formed thin film or etched. Among such apparatuses, for example, when a parallel plate plasma apparatus is used, a silicon wafer to be treated is placed on a lower electrode side, a reaction gas is distributed from an upper electrode side, which is parallel to the lower electrode, and high frequency plasma is generated by applying high frequency voltage to both electrodes, so that the silicon wafer can be etched.
As for such a plasma apparatus, in order to maintain even characteristics of a semiconductor device to be fabricated on the surface of a silicon wafer, plasma supplied to a silicon wafer has to be uniformed. Therefore, it has been conventionally devised that a circular part what is called focus ring is placed around a wafer. For example, it has been performed that since a focus ring consisting of a conductor such as graphite is placed, plasma is extended to outside of the wafer so as to improve uniformity of plasma applied to the wafer. However, this focus ring itself is also etched by plasma while the silicon wafer is etched.
Conventionally, a focus ring has been made of high purified graphite material, which has conductivity, high chemical stability, and low influence to contaminate a silicon wafer with metallic impurities. However, the graphite material is complex of particles consisting of aggregate and matrix, there may be problems such that constitutive particles are scattered and consumed due to plasma etching, and the particles fall on a silicon wafer to be treated, which may lead to trouble in formation of circuit pattern. To solve these problems, glassy carbon has been used for focus ring material recently.
However, even if the glassy carbon is used for the focus ring, the silicon wafer can not be prevented from contamination. In fabrication of a semiconductor device, contamination of a silicon wafer may cause to degrade its characteristics and lower device yield. Accordingly, it has been proposed that material of a focus ring is replaced glassy carbon causing contamination with single crystal silicon, which is the same material as a silicon wafer.
However, even if a focus ring is made of single crystal silicon with high purity as a whole, it is inevitable in forming process of a single crystal silicon plate sliced from a single crystal silicon ingot that impurities generating from a processing apparatus adhere to the surface of a focus ring when machining cut or polishing process is performed. These impurities are also generated from such as materials or tools used in each of processing apparatus, and they are mainly heavy metal. Even a small amount of such impurities cause a serious problem in fabrication process of a semiconductor device. That is, if the focus ring to which impurities adhere is used continuously, there is a problem that these impurities float and fall onto a silicon wafer, and cause to lower the yield in a semiconductor device fabricated on a silicon wafer. Also, the focus ring may be contaminated by a small amount of such as heavy metal in a plasma etching process itself.
Moreover, there is a problem that these impurities of heavy metal adhering a focus ring not only adhere to the surface of the focus ring but also diffuse inside the focus ring, so that defects are generated. Such impurities of heavy metal can be confirmed as pits by breaking a focus ring to which impurities are adhered, subjecting its broken section to such as Secco etching, and observing it under a microscope. These defects due to such impurities cause to generate particles on a focus ring and to lower a life.
The present invention has been accomplished to solve the above-mentioned problems, and an object of the present invention is to provide a silicon focus ring consisting of single crystal silicon used as a focus ring in a plasma apparatus wherein disadvantages due to impurities of such as heavy metal can be prevented.
To achieve the above-mentioned object, the present invention provides a focus ring consisting of single crystal silicon used as a focus ring in a plasma apparatus wherein concentration of interstitial oxygen in a silicon focus ring is not less than 5xc3x971017 atoms/cm3 and not more than 1.5xc3x971018 atoms/cm3.
As described above, when such a silicon focus ring of which interstitial oxygen concentration is not less than 5xc3x971017 atoms/cm3 and not more than 1.5xc3x971018 atoms/cm3 is used as a focus ring in a plasma apparatus, for example, a sufficient amount of oxygen precipitation is generated in a bulk portion of a focus ring at a high temperature, the effect, which can capture impurities such as heavy metal adhered to a silicon focus ring, what is called, intrinsic gettering effect (IG effect), can be obtained sufficiently. Therefore, the focus ring has gettering effect, and disadvantage such that impurities adhered to the focus ring fall on a silicon-wafer to be treated can be prevented. Moreover, defects due to such impurities on the surface portion of the silicon focus ring can be suppressed by the gettering effect, as the result of this, generation of particles on the focus ring surface can be reduced. Furthermore, if oxygen concentration is in the aforementioned range, defects due to oxygen precipitation such as OSF (oxidation induced staking fault) are not generated by excessive oxide precipitation during use of the focus ring, and as the result of this, generation of roughness causing particles on the focus ring surface can be prevented.
It is desirable that nitrogen concentration in the silicon focus ring is not less than 5xc3x971013 number/cm3 and not more than 5xc3x971015 number/cm3.
As described above, if nitrogen concentration in the silicon focus ring is not less than 5xc3x971013 number/cm3 and not more than 5xc3x971015 number/cm3, oxygen precipitation in a bulk portion of the silicon focus ring is promoted sufficiently, and gettering effect can be more effective.
Further, it is desirable that the surface of the silicon focus ring is subjected to etching treatment.
As described above, if the surface of the silicon focus ring is subjected to etching treatment, mechanical damage layer generated in forming process of a silicon focus ring can be eliminated, generation of particles can be reduced, and there are few adhered heavy metal.
Also, the present invention provides a producing method for a silicon focus ring used for a plasma apparatus, wherein a single crystal silicon wherein concentration of interstitial oxygen is not less than 5xc3x971017 atoms/cm3 and not more than 1.5xc3x971018 atoms/cm3is grown by a Czochralski method, the single crystal silicon is processed in a circle, and a silicon focus ring is produced.
As described above, in the producing method for a silicon focus ring, the single crystal silicon having predetermined concentration of interstitial oxygen is grown by a Czochralski method, the single crystal silicon is processed in a circle, and the silicon focus ring is produced. As the result of this, the silicon focus ring, which can be prevented disadvantages due to impurities such as heavy metal by a simple method, can be produced.
In this case, it is desirable that a single crystal silicon is grown by a Czochralski method with doping nitrogen, so that nitrogen concentration of the silicon is not less than 5xc3x971013 number/cm3 and not more than 5xc3x971015 number/cm3.
It is because gettering effect of a silicon focus ring to be produced is higher, and disadvantages due to impurities such as heavy metal can be prevented.
As described above, according to the present invention, since concentration of interstitial oxygen contained in a silicon focus ring consisting of silicon single crystal used as a focus ring in a plasma apparatus is not less than 5xc3x971017 atoms/cm3 and not more than 1.5xc3x971018 atoms/cm3, sufficient gettering effect can be afforded to the silicon focus ring. Accordingly, disadvantages due to impurities such as heavy metal can be prevented, and the yield in fabrication of a semiconductor device can be improved.